Many conventional optical receivers are hybrid circuits having silicon-based electronics and associated Ge or GainAsP-based photonics. These conventional receivers are often designed to detect the wavelengths in the range of 1.3 micrometers to 1.5 micrometers. The detection of radiation having these wavelengths is especially desirable in that high speed fiber optic-based communications networks employ these wavelengths.
However, the use of hybrid devices is undesirable for a number of reasons, including high cost, large package size, speed limitations, and decreased reliability. A preferred optical receiver would include integrated electronic and photonic devices fabricated from one material, or from lattice-matched heterostructures such as InP/InGaAsP and InP/InAlAsP. Unfortunately, progress in the development of InP-based integrated receivers has been slow.
One attractive alternative to InP-based material is GaAs. Because of the considerable effort that has been directed towards the development of this material, high performance GaAs-based integrated electronic circuits and receivers may now be fabricated reliably. Unfortunately, conventional GaAs detectors are not sensitive to radiation in the 1.3 micrometer to 1.6 micrometer range of interest.
As such, it is one object of this invention to provide a room temperature GaAs-based optical receiver that is sensitive to radiation in the 1.3 micrometer to 1.6 micrometer range of interest.
Recently, it has been reported that GaAs grown at 200-250C yields a substrate which virtually eliminates the effects of backgating and sidegating in GaAs circuits. Backgating is a dependence of a transistor's drain-to-source current on the substrate bias, while sidegating is a dependence of the transistor's drain-to-source current on the bias of a proximate device.
Specifically, in an article entitled "New MBE Buffer Used to Eliminate Backgating in GaAs MESFET's", IEEE Electron Device Letters, Vol 9, No. 2, February 1988, F. W. Smith et al. disclose a buffer layer that eliminates backgating between MESFET's fabricated in active layers grown upon the buffer layer. The buffer layer was grown by molecular beam epitaxy (MBE) at low substrate temperatures (150.degree.-300.degree. C.) using Ga and As.sub.4 beam fluxes.
In an article entitled "Infrared Response from Metallic Particles Embedded in a Single-Crystal Si Matrix: The Layered Internal Photoemission Sensor" Appl. Phys. Lett. 57(14) Oct. 1, 1990, by R. W. Fathauer et al. there is disclosed the 77K detection of infrared radiation at wavelengths of 1-2 micrometers with a device referred to as a layered internal photoemission sensor. The device structure was grown by a Si MBE technique to incorporate epitaxial CoSi.sub.2 particles, the particles having dimensions of 10-50 nanometers. Radiation absorbed by the particles is said to photoexcite carriers into a surrounding single-crystal, but highly defected, silicon matrix. A peak quantum efficiency of 1.2% was measured. However, this device exhibited, at 77K, a substantial dark current of 0.6 mA/cm.sup.2 at one volt of reverse bias. The device is not reported to operate at room temperature (295K).
In an article entitled "Effect of GaAs Buffer Layer Grown at Low Substrate Temperatures on a High-Electron-Mobility Modulation-Doped Two-Dimensional Electron Gas", Appl. Phys. Lett. 54(10) Mar. 6, 1989, by R. Melloch, et al., sidegating in GaAs integrated circuits is said to be eliminated in a MBE-grown structure with the incorporation of a GaAs buffer layer grown at low substrate temperatures (200.degree.-300.degree. C). The low temperature buffer layer is referred to as a LTBL. No deleterious effect on mobility or carrier density was said to be observed with the incorporation of the LTBL.
In an article entitled "Structural Properties of As-Rich GaAs Grown by Molecular Beam Epitaxy at Low Temperatures", Appl Phys Lett 54(19) May 8, 1989, by M. Kaminska et al., it is reported that GaAs layers grown by MBE at substrate temperatures between 200.degree. and 300.degree. C. were studied using transmission electron microscopy (TEM), x-ray diffraction, and electron paramagnetic resonance (EPR) techniques. High-resolution TEM cross-sectional images are said to show a high degree of crystalline perfection of these layers. For a layer grown at 200.degree. C. and unannealed, x-ray diffraction revealed a 0.1% increase in the lattice parameter in comparison with bulk GaAs. For the same layer, EPR was said to detect arsenic antisite donor defects (arsenic atoms on a Ga site) with a concentration as high as 5.times.10.sup.18 cm.sup.3. This observation is said by the authors to be the first observation of antisite donor defects in MBE-grown GaAs. These results are said to be related to off-stoichiometric, strongly As-rich growth, that is possible only at such low growth temperatures. These findings are said to be relevant to the specific electrical properties of low-temperature MBE-grown GaAs layers. In an article entitled "Optically Induced Reordering of As Cluster Defects in Semiinsulating GaAs", Cryst. Latt. Def. and Amorph. Mat., 1987, Vol. 17, pp. 199-204, by J. Jimenez et al., the EL2 level in GaAs is said to be associated with the existence of arsenic-rich aggregates. The EL2 level is a main midgap energy level that ensures the compensation of background shallow acceptors. This level is characterized by the existence of metastable state, which is induced by optical excitation at low temperature (T&lt;120 K). These authors report that the recovery of the normal state cannot be accomplished by optical excitation, but that a recovery of the photoconductivity signal is observed. An analysis of this phenomenon is said to reveal the existence of more than only a metastable state induced by 1-1.25 eV photons; these results are said to be based on an optically induced reordering of arsenic-rich aggregates when AsGa antisite donors are photoionized. Small differences in the AsGa complexes, inside the aggregates, are said to produce significant differences in metastability.
What is not taught by these journal articles, and what is thus another object of the invention to provide, is a GaAs material that includes metallic precipitates that overcomes the deficiency of conventional GaAs material, enabling the room temperature detection of radiation in the 1.3 micrometer to 1.6 micrometer range of interest.
It is another object of this invention to provide embodiments of photodetectors comprised of GaAs material that include As precipitates or inclusions (GaAs:As) for detecting radiation having a wavelength equal to or less than approximately 1.6 micrometers.
It is a further object of the invention to provide a P-intrinsic-N (PIN) photodiode comprised of GaAs:As material that exhibits a level of quantum efficiency (QE) and dark current suitable, at room temperature, for detecting radiation in the 1.3 micrometer to 1.6 micrometer range of interest.
It is one further object of the invention to provide an intrinsic-like body of a compound semiconductor that contains a significant concentration of acceptor or donor dopants while maintaining a substantially non-conducting electrical characteristic.